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Abstract

The structure of the title compound, (C10H10N3)2[ZnCl4], is composed of C10H9N3H+ (DPAH+) cations and [ZnCl4]2− anions. The two pyridyl rings of DPAH+ are approximately coplanar, with a dihedral angle of 7.2 (2)° between their corresponding least-squares planes. The proton is disordered in a one-to-one ratio over the two chemically equivalent pyridyl N atoms. An intra­molecular hydrogen bond is formed between the pyridinium H atom and the pyridyl N atom of the other pyridyl ring. The Zn atom lies on a twofold rotation axis. There are also some weak N—HCl hydrogen bonds. These inter­actions lead to the formation of an alternating zigzag chain in the solid state. The results clearly show that reducing agents normally used in hydro­thermal syntheses, such as metallic zinc employed here, are also active in terms of coordination chemistry.

Acknowledgments

The authors thank the X-ray Laboratory of the University of Chile for the data collection. The authors acknowledge FONDAP (grant No. 11980002) for financial support.

supplementary crystallographic
information

Comment

Core to the crystal engineering of supramolecular compounds are the different
strategies that are used to control the molecular aggregation processes. For
example, the selection of metal ions that promote the formation of extended
arrays, and organic molecules capable of forming hydrogen bonding or close
packed structures are fundamental to control the molecular aggregation (Guillon
et al., 2000, Rice et al., 2002). Therefore, the
strategies
adopted in the preparation of crystal structures involve two main concepts.
One of them is related with the use of the shape-controlled close packing of
molecules, and the second one with the use of the specific interactions to
control aggregation of molecular species (Guillon et al., 2000).

In this work we inform on the synthesis of a novel crystal structure with a
tetrachlorozincate anion obtained by hydrothermal synthesis.
The reaction conditions described in the experimental section lead to the
oxidation of the metallic zinc used as the reducing agent and, to the formation
of a crystalline tetrahalide species, which is present together with the
cationic counterion, DPAH+.

The organic cation (DPAH+) exhibits two pyridinium rings in a highly planar
arrangement with a dihedral angle between them of only 7.2 (2)°. This is
consistent with the value observed for the isostructural cobalt derivative
(DPAH+)2[CoCl4]2- of the title compound (Visser et al.,
1997);
both compounds being isostructural. The
pyridinium nitrogen atoms on the cation are in a "face to face" (or U)
arrangement, allowing the existence of an intramolecular hydrogen bond (see
hydrogen bonding table), also observed for other
2-(pyridin-2-ylamino)pyridinium
salts such as the Cl-, squarate (C4O4H)-, tetraphenylborate
(B(C6H5)4)- (Bock et al., 1998) or NO3- (Du & Zhao,
2004)
compounds.
The parameters for this interaction within these salts are basically identical.
A different situation is observed for (DPAH2+)[CuCl4]2- (Willett,
1995)
and (DPAH2+)(CF3SO3)- (Bock et al., 1998) where the
molecule is
diprotonated, leading to an S-like conformation which precludes
intramolecular hydrogen bonding.

As expected, the tetrachlorozincate anion, with the zinc atom lying on the
twofold axis, displays an almost perfect tetrahedral coordination environment.
The [ZnCl4]2-anion interacts with the cations through weak hydrogen bonds
between Cl1 and Cl2 with the DPAH+ cations, as summarized in the hydrogen
bonding table and depicted in Figure 1. Each tetrachlorozincate anion is
bonded in this way to four cations. This differs from what is observed in
(DPAH2+)[CuCl4]2-, where the values N(amine)···Cl = 2.133 Å,
N(pyridinium)···Cl = 2.307, 2.470 Å) suggest stronger interactions.
The rather strong
distortion from square planar geometry in this latter molecule has been
addressed to the hydrogen bonding interactions (Willett, 1995).

As can be seen in Figure 1, there are two pairs of strictly parallel cations,
which are separated by approximately 3.3 Å, a value that is in the range for
π-π interactions (Marinescu et al., 2005), but somewhat
shorter than
the 3.534 (5) Å reported for (DPAH+)NO3-(Du & Zhao,
2004). Each pair of DPAH+cations is in connected with a neighboring
pair in a
"head to tail" fashion (see Figure 1), thus leading to a packing arrangement
with a zigzag chain with alternating organic cations and tetrachlorozincate
anions as seen in Figure 2. These chains interact in the solid by means of
π-π contacts.

Experimental

The compound was obtained by hydrothermal synthesis employing the following
reagents: CrCl3.6H2O, DPA, V2O5, Zn, H3PO4 (85%) and H2O
(all Aldrich, used without further purification) in the following quantities:
0.1523 g, 0.28 g, 0.1438 g, 0.1054 g, 0.58 ml and 5 ml respectively. This
mixture was sealed in a 23 ml PTFE-lined stainless steel autoclave, and heated
to 393 K (120°C) for 72 h. The yield of the studied compound was
approximately 10%, and X-ray quality crystals were directly selected from
the bulk mixture of products.

Refinement

The hydrogen atoms positions were calculated after each cycle of refinement with
SHELXL (Bruker,1999) using a riding model with C—H distance
equal to
0.96 Å. Uiso(H) values were set equal to 1.2Ueq of the
parent carbon atom. At the final stages of refinement, the hydrogen bonded to
the nitrogen atoms becomes evident in the Fourier Difference Map, with some
disorder. This was modeled considering two half-occupied hydrogen sites, one
on each pyridyl nitrogen atom. These N—H hydrogen atoms were then refined
using a riding model with
C—N—H angles idealized for amide H atoms, but the the N—H
distances were allowed to refine freely.

Figures

Molecular drawing for I showing hydrogen bonding between [ZnCl4]2-and the organic cation. Atom numbering scheme is included. Displacement ellipsoids at 20%. The second hydrogen position H3N is not included in the diagram for clarity. Symmetry codes: A:...

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.